Various types of fluidization processes have been used for many years for a number of different operations and/or processes. In general, in fluidized systems a solid phase is suspended in an upwardly moving gas stream.
High turbulence existing in a fluidized bed provides high heat transfer characteristics, and can cause almost complete mixing of the solids with the fluidizing gas to form a relatively homogeneous gas-solid system.
The occurrence of channeling, caused by the formation of pockets in the solid phase, can result in the passage of gas through the solids without there being intimate contact with the solid phase.
Channeling is partially minimized by the use of a plurality of tubular zones through which the fluidizing gas is passed in contact with the solid phase. Each tube operates as an individual fluidized bed having a much smaller cross sectional area, and, overall, such tubular bed systems have greater heat transfer characteristics because of increased surface area availability.
Materials having cohesive characteristics have a tendency to form aggregates during fluidization in tubular zones and may therefore be difficult to fluidize. Starch is an example of such a cohesive material, and it tends to form lumps or agglomerates within fluidized bed reactors resulting in severe channeling and incomplete conversion of the starch.